1. Field of the Invention
The present invention relates to a process for the separation of two isomers and to the application of such process for the purification of 1-phenyl-2-bromoethane.
2. Description of the Prior Art
1-Phenyl-2-bromoethane (C.sub.6 H.sub.5 --CH.sub.2 --CH.sub.2 Br), or phenethyl bromide, is a known intermediate used in a variety of organic syntheses; it is prepared by the free radical hydrobromination of styrene with gaseous hydrobromic acid: ##STR1##
This anti-Markovnikov-type addition is promoted by the simultaneous introduction of air and gaseous HBr into styrene dissolved in a slightly polar inert solvent, such as carbon tetrachloride. The Markovnikov-type addition: ##STR2## competes with the first reaction, which is never totally selective, the significance of said competing reaction increasing with the concentration of styrene in CCl.sub.4. This reaction is, moreover, promoted by the presence of metallic impurities, such as iron.
The separation of phenethyl bromide from its -bromo-1-phenylethane isomer is difficult to accomplish by distillation in view of the small difference in the respective boiling points: 217.degree. C. for phenethyl bromide and 203.degree. C. for 1-bromo-1-phenylethane.
U.S. Pat. No. 3,058,892 describes treating the mixture of phenethyl bromide and its isomer with zinc oxide at a temperature ranging from 100.degree. C. to 150.C in order to selectively decompose the isomer. It is recommended to minimize the temperature and the reaction time in order to prevent the decomposition of the phenethyl bromide.